The study of signal transduction pathways in normal and pathological states is of considerable interest because of the potential therapeutic benefit arising from new molecular agents targeting certain of these pathways associated with disease.
Receptor tyrosine kinases (RTKs) are key enzymes in signal transduction pathways that catalyse the autophosphorylation of tyrosine residues within the cytosolic, C-terminal domain of the protein. This generates docking sites for the recruitment of downstream proteins and the subsequent propagation of signals involved in an array of cellular events including growth, proliferation and survival. More generally deregulated kinase signalling is implicated in a diverse range of pathological states including immunological and inflammatory disorders, cardiovascular and neurodegenerative disease. The known receptor tyrosine kinases encompass 20 families and many are oncogenes (Blume-Jensen P et al. 2001. Nature 411 355-365). c-Met is the prototypic member of a subfamily of RTKs which includes the related proteins Ron (macrophage-stimulating protein receptor) and its chicken orthologue, Sea. The endogenous ligand is the growth and motility factor hepatocyte growth factor (HGF, also known as Scatter Factor). c-Met and HGF are expressed in a range of tissue types although their expression is normally restricted to cells of epithelial and mesenchymal origin. In contrast, tumour cells often express constitutively activated c-Met.
There is now a growing body of compelling evidence from both animal studies and cancer patients that HGF-Met signalling plays an important role in the development and progression of malignancy and is associated in particular with invasive phenotypes. c-Met and HGF are highly expressed relative to surrounding tissue in numerous cancers and their expression correlates with poor patient prognosis (Jiang, W et al. 1999 Crit. Rev. Oncol.-hematol., 29, 209-248.) Activating point mutations in the kinase domain of c-Met are implicated in the cause of sporadic and hereditary forms of papillary renal carcinoma (Danilkovitch-Miagkova, A et al 2002. 1 J. Clin. Invest. 109, 863-867). c-Met is a marker for both cancer and malignancy and agents that inhibit c-Met-HGF signalling can be expected to ameliorate disease progression in relevant cancers.